A known method for establishing a communication between two devices via a server is based on using a unique identifier. The devices have each a touch screen or a keyboard for entering the unique identifier. In order to establish the communication the same unique identifier is entered to each of the two devices and each of the two devices transmits the unique identifier to the server. When the server receives the unique identifier from the two devices, the server establishes the communication between them.
The known method has a security problem. Since the unique identifier is entered via the touch screen or the keyboard, there is a risk that an unwanted third party will observe the entering of the unique identifier, whereby the unique identifier is compromised. Once compromised, the unique identifier can be used by the third party to establish unwanted communication with one of the two devices.